The present invention relates to an apparatus for detecting the opening of the throttle valve of an internal combustion engine.
An engine equipped with an electronic fuel injection device determines the amount of fuel injected while measuring the amount of air flowing into the engine, in order to obtain a desired air-fuel ratio.
In some engines, an airflow meter is installed in the suction passage to directly measure the amount of air sucked in. In other engines, the amount of air that is sucked in is determined from the opening of the throttle valve or the negative pressure due to suction and from the engine speed. Of the latter type, the engine which determines the engine load by detecting the opening of the throttle valve interlocking with the accelerator pedal has the advantage that it is simple in structure.
Some of the engines equipped with airflow meters are designed to detect the opening of the throttle valve for various purposes.
FIG. 1 shows a sensor for detecting the opening of a throttle valve, the sensor being disclosed in Japanese Utility Model Laid-Open No. 70104/1983, for example. This sensor comprises a case 1, a guide member 2, a connector 3, a cover 4, a potentiometer chamber 5, a driving shaft 6, a hole 7 formed along the axis of the shaft, an annular member 8, an insulating base 12 fixed to the case 1, sliders 13, a conductive sheet and a resistor sheet 14, and an output terminal 15.
The guide member 2 is fitted in a hole formed in the center of the case 1. The driving shaft 6 having the hole 7 is rotatably inserted in the guide member 2. The annular member 8 is rotatably mounted on the guide member 2, and has a protruding portion 8a. The shaft 6 has an arm 6a held in the protruding portion 8a. Thus, when the shaft 6 rotates inside the hole formed in the center of the guide member 2, the annular member 8 rotates around the guide member 2. The sliders 13 are carried on the annular member 8. The conductive sheet and the resistor sheet 14 are mounted on the insulating base 12 so as to draw an arc. Therefore, an output voltage that varies according to the angular position of the annular member 8 appears at the output terminal 15 on the principle of a potentiometer.
The sensor constructed as described above is mounted to a throttle body (not shown) to constitute an apparatus for detecting the opening of a throttle valve (not shown). A valve shaft (not shown) on which the throttle valve is carried aligns with the hole 7 in the shaft 6.
Since the conventional apparatus for detecting the throttle valve opening is constructed as described above, it is necessary to mount the case 1 to the throttle body in such a way that the valve shaft carrying the throttle valve aligns with the hole 7, otherwise the center of rotation of the driving shaft of the sensor would deviate from the axis of the throttle valve or would be inclined relative to the axis, thereby distorting the guide member 2. This would make the pressure applied to the sliders 13 by the conductive sheet and the resistor sheet 14 nonuniform. As a result, the output voltage appearing at the output terminal 15 would not be precisely in proportion to the angular position of the annular member 8. Also, vibration would be directly transmitted to the sensing section from the valve shaft, because the valve shaft is fitted in the hole 7. This would produce undesirable results.
The present invention has been made to solve the foregoing problems with the prior art apparatus. It is an object of the present invention to provide a throttle valve opening-detecting apparatus which allows the axis of the shaft of a throttle valve to deviate from the axis of the driving shaft of a sensor for detecting the throttle valve opening, and in which vibration is not easily transmitted from the valve shaft to the sensor.